Deviation from symmetry and earthquake effect on dynamic loaded foundations

Dynamic loaded foundations are systems that are composed of machine, foundation and supports. Forces affecting dynamic loaded foundations are combinations of dynamic and static loads. For this reason, besides system endurance, vibrations should be analyzed in the design. To control vibrations is ensured through guarding against resonance and keeping amplitudes lower than allowable limit values. While only one equation of motion is enough for finding vertical vibrations on a symmetric system, other vibration modes are taken into consideration in asymmetric systems. Accordingly, symmetric systems are preferred for calculation ease in designs. However, planned symmetry cannot be always kept up during/after production. Reasons, such as difference between current and planned place of machine and damages of support elements during/after production, cause deviation from symmetry as a result of changes in mass and rigidity centers. Earthquake effects must be taken into consideration in addition to static and dynamic loads in design. Ground motions combining with machine vibrations may cause damage even demolish the structures. Lots of earthquake around the world have damaged machine foundations. Besides foundations, these damages also occurred in machine and equipment because of vibrations transmitted from foundations. A new machine may be set up on an old foundation. For this reason; weight of the machine, amplitude and angular frequency of exciting force may be different than previous one. In this study; angular free vibration frequencies and vibration amplitudes of dynamic loaded foundations for symmetry, deviation from symmetry, applied ground motion, new machine installation cases, are calculated.